The EFG analysis of La2CuO4 and YBa2Cu3O7 based superconductors

It is shown that the 3d3z2-r2 orbital of the in-plane copper and the 2pz apex oxygen orbital are absent at the Fermi level of La2-xSrxCuO4, at variance with proposals giving importance to copper-apex oxygen hybridization. At the in-plane oxygen site a sizable 2pz admixture is found at the Fermi level of YBa2Cu3O7. The additional holes are shared among copper and oxygen sites in similar proportions. This is shown compatible with the large Ud Emery model provided that the difference between the p and d atomic energies is comparable to the first neighbor overlap energy. (orig.)